Recently, repairing materials, like bone cement, become increasingly important in bone treatment. In particular, the treatment methods applied in vertebral support and vertebroplasty for preventing compression on spinal cord can further replace traditional nerve decompression operations or combine with traditional spinal fixation operations to solve nerve compression. In addition to higher patient acceptance, this treatment method is further applied extensively to treating compressive fracture due to various primary and secondary osteoporosis and reinforcing vertebral stability.
The minimally invasive surgery of vertebroplasty is performed in vertebral columns using percutaneous puncture technique. By introducing repairing materials into damaged vertebral columns, the strength of the vertebral columns and vertebral stability can be enhanced. Besides, patients' chronic pains caused by the damaged vertebral columns can be reduced as well. The Poly-methyl methacrylate (PMMA) is the mainly adopted as the repairing materials.
In order to inject repairing materials into damaged vertebral columns, the injection devices for repairing materials become extremely important. The stability of injection rate, the convenience in applying force, and the adaptation to other devices impose direct influences on the efficacy of injection devices. They also determine indirectly the success of surgery outcomes. Currently, the majority of injection devices for repairing materials are syringes. A repairing material is placed in a syringe having a special injection needle disposed at the injection passage. Then, like normal injections, the piston is used to compress and inject the repairing material inside the syringe into the target bone through the specially designed injection needle. Nonetheless, in the injection method, the resistance of pushing and compressing the piston will become increasingly greater because the repairing material will coagulate gradually during the injection process. Under the circumstance, it is difficult to inject the repairing material; the injection rate will change from fast to slow. Then the injected repairing material is fewer than expected and thus affecting the efficacy of the surgery.
Recently, the adopted repairing materials with thermoplastic are commonly used in biological tissue repair as well, which means that the repairing materials are softened and transformed to be fluid by heating and become plastic. After cooling, they recover to be solid and thus reinforcing the strength and stability of vertebral columns. The molecular chains of this type of material are mostly linear or structures having sub-chains. Thereby, by physical changes, the materials can be softened by heating and hardened by cooling. In particular, poly(D, L-lactic-co-glycolic) acid (PLGA) is the mainly adopted as the repairing materials with thermoplastic.
Furthermore, in order to place repairing materials into damaged vertebral columns successfully, according to the existing techniques, the bone material to be injected should be molten completely. Then the molten repairing material should be loaded into the injection device before the repairing material is injected into bones for reinforcing the bone structure. Nonetheless, by using this method, heating the repairing material at relatively higher temperatures and longer time might damage the repairing material. Besides, because the repairing material starts to coagulate shortly after it is molten completely, the imposed time limit in the process from melting to injection will be totally depend on material properties. This time limit results in lower adaptability in a surgery process that might vary from minute to minute. Consequently, this will bring inconvenience for doctors in surgeries and hence affecting surgery outcome.
Accordingly, how to design an injection device having the properties of convenient operations, stable injection rates, and real-time heating capability for repairing materials has become a major subject in the field.